The present invention relates to a positive resist composition suitable for use in microlithography processes such as the production of ULSIs or high-capacity microchips and in other photofabrication processes. More particularly, the invention relates to a chemical amplification type resist composition capable of forming a high-resolution pattern with a vacuum ultraviolet light having a wavelength of 160 nm or shorter.
The degree of integration in integrated circuits is increasing more and more, and it has become necessary to form an ultrafine pattern having a line width of a quarter micrometer or smaller in the production of semiconductor substrates for ULSIs or the like. One of the known techniques for enhancing the fineness of such patterns is to use an exposure light source having a shorter wavelength in resist pattern formation.
For example, in the production of semiconductor elements having an integration degree of up to 64 megabits, the i-line (365 nm) from a high-pressure mercury lamp has hitherto been used as an exposure light. Many compositions comprising a novolak resin and a naphthoquinonediazide compound as a photosensitive substance have been developed as positive resists for use with the exposure light, and have given sufficient results in forming patterns having line widths down to about 0.3 xcexcm. On the other hand, in the production of semiconductor elements having an integration degree of 256 megabits or higher, KrF excimer laser beam (248 nm) has been used as an exposure light in place of the i-line.
Furthermore, use of ArF excimer laser beam (193 nm), which is an exposure light having an even shorter wavelength, and use of F2 excimer laser beam (157 nm) for forming a pattern having a line width of 0.1 xcexcm or smaller are recently being investigated for the purpose of producing semiconductor elements having an integration degree of 1 gigabit or higher.
With the use of such exposure lights having shorter wavelengths, the components of resist materials and the structures of compounds for use therein are changing considerably.
A so-called chemical amplification type resist has been developed as a resist composition for exposure to KrF excimer laser beam. This composition comprises a combination of: a resin, as the main component, having a poly(hydroxystyrene) backbone which shows reduced absorption in a 248 nm region and is protected by acid-decomposable groups; and a compound which generates an acid upon irradiation with far ultraviolet light (photo-acid generator).
Furthermore, another chemical amplification type resist has been developed as a resist composition for exposure to ArF excimer laser beam (193 nm). This composition contains an acid-decomposable resin which has, incorporated in the polymer main chain or side chains thereof, alicyclic structures showing no absorption at 193 nm.
With respect to use with F2 excimer laser beam (157 nm), even the alicyclic resin shown above was found to be insufficient in obtaining a desired pattern of 0.1 xcexcm or finer because the resin shows considerable absorption in a 157 nm region. Under these circumstances, a resin having fluorine atoms (perfluorinated structure) incorporated therein was reported to have sufficient transparency at 157 nm, in Proc. SPIE., Vol.3678, p.13 (1999). Effective structures of such fluororesins are proposed in Proc. SPIE., Vol.3999, p.330(2000), p.357 (2000), and p.365 (2000) and in WO-00/17712, etc. Resist compositions containing a fluorine-containing resin have come to be investigated.
However, the fluororesin-containing resist compositions for exposure to F2 excimer laser beam have problems concerning line edge roughness, etching rate, etc., and elimination of these problems have been desired.
Line edge roughness means a phenomenon in which resist line edges located at the interface between the resist line pattern and the substrate have a contour irregularly rugged in directions perpendicular to the line direction due to properties of the resist. When this pattern is viewed from right above, edges having recesses and protrusions (xc2x1about from several nanometers to tens of nanometers) are observed. Since these recesses and protrusions are transferred to the substrate in an etching step, large recesses and protrusions cause electrical failures, resulting in a reduced yield.
Accordingly, an object of the invention is to provide a chemical amplification type resist composition suitable for use with an exposure light source having a wavelength of 160 nm or shorter, in particular, F2 excimer laser beam (157 nm). Specifically, the object is to provide a chemical amplification type resist composition which is sufficiently transparent to the exposure light having a wavelength of 157 nm, has high etching resistance, and is reduced in line edge roughness.
The present inventors made intensive investigations in view of the properties described above. As a result, they have found that the object of the invention is accomplished by the following specific composition. The invention has thus been achieved.
The invention has the following constitutions.
(1) A chemical amplification type resist composition comprising:
(a) a resin comprising repeating units having a side chain containing a partial structure represented by the following formula (I) and which increases the solubility in an alkaline developing solution by the action of an acid,
(b) a compound capable of generating an acid upon irradiation with actinic rays or a radiation,
(c) a low-molecular compound having a molecular weight of 3,000 or lower, wherein the value determined with the following calculation formula (1) is from 0.1 to 0.5:
[(number of carbon atoms)xe2x88x92(number of oxygen atoms)xe2x88x920.5xc3x97(number of fluorine atoms)]/(number of all atoms) xe2x80x83xe2x80x83(1)
xe2x80x83and
(d) a solvent: 
wherein R50 to R55 each independently represents a hydrogen atom, a fluorine atom, or a fluoroalkyl group, provided that not all of R50 to R55 simultaneously represent hydrogen atoms and that R55 may be bonded to an atom of the main chain of the resin through a connecting group or directly,
R1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms,
W represents an organic group having 6 to 30 carbon atoms, and
n represents an integer of 0 to 4.
(2) The composition according to the above (1), wherein the partial structures contained in side chains of the resin are represented by the following formula (Ixe2x80x2): 
wherein R50 to R55 each independently represents a hydrogen atom, a fluorine atom, or a fluoroalkyl group, provided that not all of R50 to R55 simultaneously represent hydrogen atoms,
R1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms,
W represents an organic group having 6 to 30 carbon atoms, and
n represents an integer of 0 to 4.
(3) The composition according to the above (1), further comprising a fluorine-based and/or silicon-based surfactant.
(4) The composition according to the above (1), further comprising as an acid diffusion inhibitor a basic compound having one or more nitrogen atoms.
(5) The composition according to the above (1), which is for irradiation with F2 excimer laser beam having a wavelength of 157 nm.
(6) The composition according to the above (1), wherein the content of the repeating units is 10 to 90% by mole based on the component (a).
(7) The composition according to the above (1), wherein the value determined with the formula is from 0.1 to 0.45.
(8) The composition according to the above (1), wherein the molecular weight of the component (c) is from 100 to 2500.
(9) A method for forming a pattern, which comprises forming a resist film comprising the composition described in the above (1), exposing the resist film upon irradiation with the actinic rays or a radiation, and subsequently developing the resist film.